Like Oil and Water
by summerlover21
Summary: Setting AU High school; Fionna and Marshall Lee have always been enemies since they could remember. Ever since Marshall had bullied her best friend, Bubba Gumball, at the playground, they can't stand each other. And everyone knows it. He was a bully. She, the school hero. Like oil and water, they were not meant to mix… Rated T for now, but might change in the future. Not sure.
1. Chapter 1

Authors Note: This is my very first fanfic, so bear with me please. I accept constructive criticism but no hate. If you don't like it, don't read it. I will not waste my time on people who hate me, that is just wrong!

P.S. To avoid any confusion, they are all the same age and grade.

Fionna: 17; junior

Marshall Lee: 17; junior

Gumball: 17; junior

Finn: 17; junior

Marceline: 17; junior

Yes I am adding Finn and Marceline in the story. Finn is her twin brother and Marceline is Fionna's other best friend, besides Gumball of course! Cake and Jake are in it too, but they are going to be animals. Don't judge me, it's my story, I DO WHAT I WANT! Anyways, I know, I know what you're thinking, 'shut up and get on with the story!' But never fear, Arianna is here! Onward! *points out into the distance like a weirdo*

Disclaimer: Sadly, I do not own Adventure Time or any of its characters

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Chapter 1: You're a Bully

_Ten years earlier…_

A 6-year old Fionna is sitting alone in the sand box. Her honey, blonde hair glistens in the sunlight under her bunny eared hat and her deep blue eyes stand out on her pale skin. She happily scoops sand into her bucket. She turns the bucket over, after making sure the sand had set, making a perfect sandcastle.

"Nice sandcastle, Fionna," said a boyish voice from behind her.

She gasps and jumps in surprise and quickly turns. A smile instantly grows on her face as she sees he best friend, Bubba Gumball. Gumball is not really his name but when Fionna met him, he was wearing too much pink. He looked like a gumball. His light blue eyes and strawberry blonde hair and love for sweets only egged Fionna to continue the use of his nickname.

"Hi Gumball," Fionna replied cheerfully, " do you want to help me build a sandcastle?"

Gumball scowled at the nickname. "I don't know, my mommy said that if I get my clothes dirty, I would be in trouble."

Fionna frowned. "Aw come on, Gumball, please. I even brought you an extra scoop." She pouted , holding up the extra scoop.

He sighed in defeat. "Ok, I'll help." He then smiles, grabs the extra scoop and kneels down beside her and starts piling sand inside the bucket.

The two childhood friends sat there happily, not realizing that they were being watched by another little boy from behind a tree. Unlike the two friends, this boy wore a scowl on his face. His gray eyes turned stone cold as he watched the two. He had ebony, unruly hair and pale skin, even paler than Fionna's, making him seem almost ghostly white. He blended almost perfectly into the shadows.

The boy watches as Fionna looks up at a butterfly as it floats by.

"Oh, Gumball, look at the pretty butterfly," he hears her say as he watches her get up and start chasing after the delicate insect, trying to catch it with her bare hands.

Gumball looks up from where he was and smiles at the sight of silly best friend.

"Fionna, you're never going to catch it." Gumball teases with an amused smile as Fionna glares at him.

"Oh yeah," Fionna challenges, "watch me." She turns around from him and continues with what she was doing.

While distracted, Gumball did not notice the strange shadow boy sneak up behind him until he found himself covered in sand. The boy had gone up and kicked Fionna's and Gumball's perfect sandcastle at Gumball.

Gumball's eyes start to water as he had gotten sand into them. The boy noticed this and starts to laugh a cold laugh. He picks Gumball up by his collar, only to shove down onto the sand.

"Ow," exclaims Gumball having scraped his elbow while trying to break his fall. He starts crying even more. The boy only continues to laugh.

Noticing Gumball's cry, Fionna turns around to see her best friend in tears and boy who she does not know laughing at him. Her face flushes a cherry red and her cheeks puff out in anger.

_'No one is going to hurt my best friend,' _thought Fionna as she stomped her way over to the two boys.

"Hey!" she yells as she pushes the laughing boy away from Gumball, causing him to fall. "Leave him alone!" She holds out a helping hand to Gumball. He sniffles and takes her hand allowing her to pull him up.

The shadow boy scowls at Fionna. He gets up and pushes Fionna.

"What the flip, dude! What's your problem." Fionna crosses her arms and glares at the boy as Gumball hides behind her.

"You're in _MY_ sand box, that's the problem." The boy mimics Fionna in crossing her arms and glares back.

Fionna scoffed. "_YOUR _sand box?! What the flip are talking about? It's not _YOUR _sand box, it's _EVERYONES _sand box."

It was the boy's turn to scoff. "Oh yeah," the boy challenges, "Then why does it have an _M_ on it." The boy smiles smugly as he points at a place in the corner of the box. "_M _for Marshall Lee." The boy says obnoxiously as eyes light up victoriously. He crosses his arms again.

Fionna huffs and at looks to where he is pointing. Sure enough, there is a large _M _scratched onto the wood that is the sand box.

Fionna glares back at the boy now named Marshall Lee, hands on hips, and opens her mouth to say something when Gumball interrupts.

"That-"

"Fi, let's go. I don't want any trouble." He glances at Marshall Lee. Surely Marshall was more than capable to beat him up. _'And Fionna' _he added.

Fionna's features softened at the sound of her best friend's frightened voice.

"But… he hurt you." She stares daggers at Marshall, who only smiles smugly in reply.

"_Please_," He looks at her with pleading eyes.

Fionna sighs as she shoots Marshall another piercing look. "Ok, we'll go."

Gumball sighed gratefully and takes Fionna's hand in his. Fionna's face flushes red again, but from embarrassment. Gumball never really holds her hand. He starts to drag her away when Fionna suddenly stopped.

"What about our stuff?"

"Leave it. Let's go!" Gumball tugged a little rougher this time, desperate to leave but Fionna stayed put.

"Gumball!"

"You should listen to Gumbutt over here. It's not like you'll need it." Marshall drawled and to emphasize his point, he sat down and started using their stuff.

"His name is _Not _Gumbutt!"

Marshall only shrugs and continues on with his playing.

"You're a bully!" was the last thing Fionna said to Marshall as they left the playground.


	2. Chapter 2

Author's Note: Hiiiiiiiiiiiiii! I can't believe you guys actually liked it! I mean when I posted it, I was totally freaking out! And then I saw the views. 244 EFFING VEIWS!

Like ASDFGHJKL

Anyways, if I hadn't mentioned it before, I will now. Please, please, PLEASE! R&R It would really motivate me to continue and also remind me that people actually want to read my story.

'Arianna shut up and get on with the story already! Nobody wants hear that type of fluff!' This is what my mind is telling me… Don't you think it's rude…? You know what, don't answer that.

P.S. On a more serious note, I meant to post this earlier but school has been a bitch. WHO NEEDS HOMEWORK! I ALREADY SPEND MY HALF OF MY LIFE AT SCHOOL! Luckily I had a three day weekend so I managed to finish this chapter … well most of it… I'll try to post as soon as possible because let's face it; everyone hates it when an author takes like a long ass time to update! I sure know I do! Anyway I'm rambling again. ONWARD!

P.P.S I know you must be getting mad with all these interruptions but I promise you this is the last one. I've decided that I'm making Marshall Lee and Marceline twins too. Originally, I was thinking of just making them friends but then I was like, 'They look the same might as well make them related' and then I considered making them cousins and I was like, 'Arianna, that's stupid. Don't make it hard on yourself and make them twins.' Alright now I'm done.

Disclaimer: Really you guys. You honestly believe I would own something as awesome as Adventure Time. *shakes head*

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Chapter 2: The Story begins…

(Fionna POV)

_BEEP BEEP BEEP_

Was the noise that so rudely woke me up. I groan and turn around, trying to block out the demonic noise with my pillow.

"Urg…"

I was just about to fall back asleep when I hear a pounding on my door and a muffled shout.

"Yo, Fi, we gonna be late for our first day of school!"

I sigh. There was no point in stalling anymore. Catherine would kill me if I were late, _again. _The pounding continues.

I reluctantly get out from the warmth and comfort that is my bed. My cat, Cake, mewls in protest. Her calico fur ruffles as she stretches. I smile softly and scratch behind her ears. She leans into my hand and purrs contently.

"Alright, I'm coming," I yell out, "No need to yell!"

There is a muffled scoff but the pounding does not continue. I yawn and stretch out all the chinks in my back. I giggle slightly. Doing that always reminds me of an old person.

Slowly, almost zombie-like, I make my way to my bathroom. I quickly set my shower to almost its hottest setting. I yawn again. I make my way towards my mirror, as I wait for the water to heat up. I stare at my reflection in horror. The bags under my eyes are all puffy and my hair is a crow's nest. I quickly run my fingers through my blonde locks to try and tame it but to no avail. I sigh as I notice the slight vapor that now covers the mirror.

I quickly undress and jump in. My body erupts in goose bumps as the water hits my bare skin. I shiver slightly. I lean against the wall, thinking. _'What the hell am I going to do?' _I think _'I've avoided him the whole summer but I sure as hell can't avoid him at school._' Sigh. _'I guess I have no choice.'_

I quickly finish my shower. I have no idea how long I was in there. The water was freezing by the time I got out. I walk out of the bathroom and change into my usual outfit. A light blue shirt with a darker blue skirt. I then proceed to put on my thigh high socks and Mary Janes. To finish off the outfit, I stuff my floor length hair into my famous bunny eared knitted hat that my parents gave me on my fourth birthday.

_'Before they…'_ A tear escapes my eye at the thought of my parents. _'No, Fionna, do not think about that right now.'_ I force the thought away and wipe the tear forcefully and put on a small sad smile. I breathe in deeply and walk out my room.

I hear, more like smell, my adoptive mother making my favorite breakfast. My mouth waters. I take a step toward the door leading into the kitchen when I'm suddenly pushed roughly into the wall, knocking the wind out of me.

"_BACON PANCAKES!" _yells my idiot of a twin brother, Finn, as he makes his way into the kitchen. Jake, his golden retriever, following loyally close behind. Cake, who I hadn't noticed had followed me, hissed loudly in my defense.

I get up, groaning at the pain on my side, and walk through the door. I see my brother already shoveling what was probably his fifth pancake into his already full mouth.

"Sowey 'bout boushing ou," he swallows thickly. "Bacon pancakes, ya know." He shrugs.

I roll my eyes and turn to my adoptive mother. "Mornin' Catherine." I peck her on the cheek while giving her a hug. Although I've known Catherine my whole life, I can't bring myself to call her mom. I love her and she will always be my mother but I can't help feeling that I would be dishonoring my parents if I started calling Catherine and Robert _'mom' _and _'dad'. _Finn is the one who is more comfortable with that.

"Mornin' sweety, ready for school?" She asks as she returns my hug.

"Yeah, I guess." I shrug.

She frowns and holds my shoulders at arm's length. "What's wrong?" she asks me, worried.

I force a smile, "nothing, just tired I guess."

She gives me a skeptic look but seems to buy it. She hands me a plate of the flapjacks and I sit by my brother. He leans over my plate as he tries to take a bit from pancake but I shove his face away.

"Nuh uh, fat ass, get your own." I smirk and turn away.

He pouts and looks down at himself self-consciously. "I'm not fat."

I smile slyly; he's not wrong. He's actually pretty fit for someone who eats like an elephant but am I going to admit it to him. _No_. It will only fuel his ego. Anymore, and his head will explode. Not that I care, I just don't want to be the one who has to clean his brain-guts off the walls.

He frowns and crosses his arms. I laugh but soon stop when I catch my adoptive mother's glare.

"Fionna," she says warningly. "You know I do not approve of that type of language in this house."

I look down and mumble a "sorry."

"It's alright." She then gets a playful look in her eyes as she turns to my brother. "But yes darling, I think I'm starting to see a bit blubber building up." She pokes his stomach before turning back to me and winks. I bite my lip as I try to keep myself from laughing.

_"MOM!"_

I couldn't hold it in anymore. I burst out laughing, almost falling off my chair. Finn glares at me as he shoves my shoulder. I actually fall this time, landing painfully on my butt.

"Ow."

He starts laughing and gets up to put his plate away but before he can turn around, I swipe my foot causing him to fall backwards onto his chair. He falls back with such a force that knocks his chair backwards, landing on his back.

"Ow." He groans.

I start laughing again. "Now were even," I state as I get up, holding out my hand for him to grab.

"Whatever," he grumbles as he takes my outstretched hand. Catherine, who is used to me and my brothers antics, just stands there, chuckling. She walks up to us gives us both a hug and a kiss on the cheek.

"Be good." She says in between kisses "don't cause too much trouble."

Me and Finn look at each other and smirk. We are known to attract trouble whether we want to or not.

"We won't," we say in unison.

She gives us a half-hearted glare before she pushes us out the door.

The bus ride to school was pretty much uneventful. A bunch of kids cooped up in a yellow, metal, box, throwing paper balls is to be expected. My brother is especially one these idiots. Ok, maybe I can't be the one to talk as I would usually be in on it too but I just wasn't feeling it today. I roll my eyes as I watch Finn aim at a guy named Lumpy Space Prince. Weird name, I know, but it's not my fault his parents named him such an awful name. It suits him though. He has purplish hair and is slightly lumpy.

I watch as the ball of paper leave Finn's hand and hits LSP (B.T.W. his nickname) right in the face. His face was priceless.

I try to stifle a laugh as I watch LSP drop his phone, while frantically trying to catch it.

_"WHAT THE GLOB!"_ He exclaims in his oddly high-pitched voice as he looks around for who did it.

Finn turns around quickly, trying to hold back his laughter. We look at each other in the eye before we quickly cover each other's mouth. Tears start pouring out of my eyes as hold back from laughing too hard.

Luckily we had arrived at school so we left before LSP could pursue the matter any further.

We quickly walk out of the bus without looking too suspicious. Although I did nothing wrong, I have a feeling I would get the same tongue-lashing from LSP as my brother. You don't really want to get on LSP's bad side. He may throw the best parties but can start nastiest rumors when provoked.

We walk away, still laughing, and push my brother playfully. We promised Catherine we wouldn't get in as much trouble this year but it's kind of hard when you have rumors about you flying about. He pushes back and I hold him in a head lock as I rub my fist into his scalp.

"Uncle, Uncle." He groans.

I smirk and put my hands down. I look around and spot my two best friends, _IN THE WHOLE WORLD, _Bubba and Marceline standing by the school gates. I quickly make my way towards them. You see, I've known Bubba (or Gumball as I would prefer) since I moved here when I was four. His mom is best friends with Catherine.

I met Marceline shortly after my encounter with Marshall Lee. '_UGH. Even thinking his name nauseates me.'_


End file.
